Evidently some have problems reading the title of your post.
When our Bus was new we had a leak in the gear box at the fan shaft area. Took it to Red Bay and they replaced the gear box while I watched. Aside from removing the bottom shield the only area they had problems with was getting the fan disconnected from the fan shaft. The fitting that attaches to the fan has bolts that are hard to get to. That fan mounting piece is held to the round shaft with 2? (I think) hex socket screws and a square steel key holding it to the shaft. Tiffin guys had trouble getting that loose and had to go for the bolts holding the fitting to the fan blades. When they disassembled, they said the fan would not come out if the shaft was still connected to the gear box. It took 2 techs about 3 hours to do the job, and they were working at head height on the whole coach lift. Laying on your back under it may be quite a bit tougher.
Just FYI, I have not been able to get my bottom gear box drain plug out for about the last 3-4 times it was scheduled for a lube change. Rounded the inside socket of the plug. I've been loosening the forward bearing cap since then to drain it, and have had no problems so far. If you tackle it I'd be very interested in any special problems you meet and your procedure. Although I watched Tiffin change mine, I should have paid closer attention.
Good luck.
